Fuel injection device for diesel engine

ABSTRACT

The present invention provides a wide range injection timing, small dispersion, good response and simple structure. In order to obtain this, in a fuel injection device for a diesel engine comprising a cylindrical body ( 11 ), an upper plunger ( 12 ) inserted thereto and capable of sliding in a vertical direction in response to a cam, an intermediate plunger forming a pressure chamber ( 14 ) with respect to the upper plunger, a lower plunger ( 16 ) brought into contact with the intermediate plunger, and an injection chamber ( 17 ) provided in a lower end portion of the body plunger, in which a fuel in the injection chamber is injected by the lower plunger being subject to a force from the upper plunger, the improvement comprises a passage, having a large cross-sectional area, formed in the body for supplying a pressurized oil to the pressure chamber, the intermediate plunger ( 13 ) being vertically movable in response to an oil pressure so as to make it possible to change a volume of the pressure chamber, and a timing spring ( 15 ) having an end being brought into via contact with the intermediate plunger and the other end being brought into contact with the lower plunger and vertically moving the intermediate plunger in response to the pressure.

FIELD OF THE INVENTION

The present invention relates to an injection device for a dieselengine, and more particularly to a unit injector for high pressureinjection for a diesel engine.

BACKGROUND ART

In recent years, a unit injector for a high pressure injector for highpressure injection for a diesel engine has been strongly desired inorder to improve air pollution due to the diesel engine and reduce fuelconsumption. For example, in Japanese Patent No. 2524657, there issuggested a high pressure unit fuel injector provided with a variablelength hydraulic link, for controlling an injection timing, and aninjection pressure control valve. The fuel injector achieves improvedpressure control without adversely influencing a controlled amount of atiming fluid.

FIG. 4 is a cross sectional view of a fuel injector 50 for high pressureinjection described in the publication. An upper plunger 51, subject toa drive force from a cam shaft (not shown), is closely arranged in acylinder hole 53 in such a manner as to freely slide in a verticaldirection due to an upward force by a spring 52. A timing chamber 55capable of changing a volume is formed between a lower end of the upperplunger 51 and an intermediate plunger 54. A timing fluid 56 such as afuel is supplied to the timing chamber 55 via a narrow timing fluidpassage 59 formed in an injector barrel 58. The timing fluid 56 forms ahydraulic link between the intermediate plunger 54 and the lower plunger61, and is preferably discharged under a certain condition via a firstdrain passage 62 formed in a direction of a central axis through theintermediate plunger 54. Further, the timing chamber 55 communicateswith a compensation chamber 63 via a valve mechanism 70 in a bottomportion of the first drain passage 62. The valve mechanism 70 is heldbetween the lower end portion of the intermediate plunger 54 and theupper end portion of the lower plunger 61 arranged within thecompensation chamber 63. When the valve mechanism 70 is opened, thetiming fluid 56 flows within the compensation chamber 63 from the timingchamber 55 via the first drain passage 62 and is discharged out of thefuel injector 50 via a second drain passage 64. The valve mechanism 70controls a pressure of the timing fluid 56 within the timing chamber 55,and next, the pressure controls an upper limit of the injection pressureof the fuel and a timing of the injection. The valve mechanism 70 isnormally closed by application of a force due to a timing spring 65arranged within the compensation chamber 63 and a valve spring 66arranged within the lower plunger 61. Further, the force of the timingspring 65 pulls up the lower plunger 61 and operates so that threeplungers, comprising the lower plunger 61, the intermediate plunger 54,and the upper plunger 51, are integrated until a controlled amount and atiming in the next cycle start after a completion of the injectioncycle. A supply of the timing fluid 56 to the timing chamber 55 isperformed through the narrow timing fluid passage 59. The injectiontiming is changed in accordance with a supplied amount of the timingfluid 56. For example, when the supplied amount is much, the injectiontiming is quickened. The timing spring 65 moves the lower plunger 61upwardly a degree sufficient to feed out the fuel to an injectionchamber 73 adjacent to an injection nozzle 71.

Next, when the injection timing is established by the supply of thetiming fluid 56 within the timing chamber 55, the injected fuel flowswithin the injection chamber 73 via a supply orifice 75 of a fuel supplypassage 74. The injected fuel in the injection chamber 73 is accuratelycontrolled in accordance with a known pressure/time principle. An amountof the injected fuel controlled in the above manner becomes a functionof a total control time for fluid flow through the fuel supply passage74 and a supply pressure, and the fuel supply passage 74 has a hydraulicproperty so as to give a control capacity having a desiredpressure/time.

Here, when the upper plunger 51 is driven downwardly due to a rotationof the cam, the timing fluid 56 is returned through the timing fluidpassage 59 until the timing fluid passage 59 is closed by the lowerportion of the upper plunger 51. The timing fluid 56 is trapped betweenthe intermediate plunger 54 and the upper plunger 51, so that ahydraulic link for integrally moving all three plunger elements towardthe nozzle 71, disposed on the bottom portion of the injection chamber73, is formed. During downward motion of three plunger elements, whenthe timing fluid pressure becomes more than a maximum predeterminedpressure determined by a resultant force of the valve spring 66 and thetiming spring 65, the valve mechanism 70 is opened, so that the timingfluid 56 is discharged from the timing chamber 55 through the first andsecond drain passage 62 and 64 so as to reduce a pressure to conform toa predetermined limit value. Then, the supply orifice 75 of the fuelsupply passage 74 is closed when the lower plunger 61 moves downwardly,so that a control of a fuel amount is finished. Further the lowerplunger 61 moves downwardly, thereby injecting the controlled fuel inthe injection chamber 73 from a plurality of orifices in the injectionnozzle 71 within the combustion chamber (not shown).

However, the valve mechanism 70 mentioned above has a complex structure,so that a highly accurate dimension, flatness and the like are requiredfor parts thereof. Further, since the valve mechanism 70 controls thepressure of the timing fluid 56, there is a problem in that an amount ofleakage is not fixed due to a temperature, a viscosity, and the like ofthe fluid, so that the pressure is not fixed.

Further, in the case wherein the injection timing is controlled by anamount (a volume) of the timing fluid 56 supplied within the timingchamber 55, the amount of the timing fluid 56 is controlled by amagnitude of the timing fluid passage 59 and the control time. Inaccordance with the present publication, since the timing fluid issupplied through the timing fluid passage 59 in the form of the narrowfixed orifice, the amount of the timing fluid 56 is changed by a kind, atemperature, or a viscosity of the fluid, so that the injection timingis not fixed. On the contrary, when making the timing fluid passage 59greater in cross-section, a range of the injection timing is narrowed.Further, when making the control time long, the volume of the timingchamber 55 is increased, so that there is a problem in that the fuelinjector 50 itself becomes large.

Further, when controlling a little amount of fuel under a low rotationalspeed or a no load operation, it is necessary to make the timing fluidpassage 59 of the fixed orifice narrow; however, when making it narrow,the control time becomes long in the case of intending to suddenlyincrease the fuel, so that a response of the engine is delayed.Particularly, in a vehicle having a great load change applied to theengine, such as a construction machine and the like, it is a greatdisadvantage that the response of the engine is delayed. Further, in thenarrow fixed orifice, a dispersion (i.e., statistical variance) of thediameter thereof increases a rate of a dispersion in an area of theorifice, and increases a dispersion in the injection timing and thevolume of the fuel.

In addition, the fuel to the injection chamber 73 is supplied via thesupply orifice 75 in the fuel supply passage 74. The supply orifice 75is also required to be made narrow for controlling a little amount offuel at a time of the low rotational speed or the no load operation.However, when being made narrow, the control time becomes long in thecase of intending to suddenly increase the fuel, so that there is aproblem that the response of the engine is delayed.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a fuel injection devicefor a diesel engine for solving the problems mentioned above, comprisinga high pressure injection unit for a diesel engine having a wide rangeof injection timing, little dispersion, and a good response. Inaccordance with a first invention of the present invention, there isprovided a fuel injection device for a diesel engine comprising acylindrical body, an upper plunger, closely inserted within a hole ofthe body, to slide in a vertical direction responsive to an appliedforce from a cam, an intermediate plunger arranged below the upperplunger in such a manner as to be coaxial with the upper plunger andforming a pressure chamber for a hydraulic link with respect to theupper plunger, a lower plunger arranged below the intermediate plungerin such a manner as to be brought into contact with the intermediateplunger, and an injection chamber provided in a lower end portion of thebody in which a fuel stored in the injection chamber is discharged bythe lower plunger upon receiving an applied force from the upper plungervia the hydraulic link and the intermediate plunger, the improvementcomprising:

a passage, having a large cross-sectional area, formed in the body forsupplying a pressurized oil to the pressure chamber, the intermediateplunger is adapted to vertically move in response to an oil pressure soas to make it possible to change a volume of the pressure chamber, and atiming spring, having an end in contact with the intermediate plungerand the other end in contact with the lower plunger, to vertically movethe timing plunger in response to the pressure.

In accordance with the structure mentioned above, in the case ofrotating under no load and at a low rotational speed, an oil under a lowpressure is supplied to the pressure chamber via the passage, and a fuelunder low pressure is supplied to the injection chamber. Accordingly, ina downward slide motion, only the intermediate plunger is initially sliddownward without moving the lower plunger downward, so that it ispossible to delay the injection timing.

Further, in the case that the diesel engine rotates In under a high loadand at a high rotational speed, the it pressurized oil under highpressure is supplied to the pressure chamber via the passage, and alarge amount of fuel under high pressure is supplied to the injectionchamber. Accordingly, in the downward slide motion, both theintermediate plunger and the lower plunger are immediately sliddownward, so that fuel can be injected to a combustion chamber from theinjection chamber at an early timing without delaying the injectiontiming.

As mentioned above, it is possible to obtain a delayed timing and anearly timing by a simple structure, so that a predetermined range ofinjection timing can be easily obtained. That is, an injection timinghaving a predetermined range can be obtained by a delayed predeterminedinjection timing due to a predetermined interval between theintermediate plunger and the lower plunger at a low rotational speedunder no load and an early injection timing at a high rotational speedin a state that there is no interval between the timing plunger and thelower plunger due to the pressure acting on the timing plunger at a highload.

Further, since the oil pressure and the oil amount are supplied to thepressure chamber via the passage, it is possible to quickly move to theearly injection timing, so that a response of the engine can beimproved. Further, since the timing spring is brought into contact withthe lower plunger and both of them commonly move downward, there is anadvantage that the pressure within the pressure chamber is notabnormally increased.

In accordance with a second invention, there is provided a fuelinjection device for a diesel engine as In recited in the firstinvention, wherein the timing plunger has a first hole connected to thepressure chamber at a center portion and a second hole communicated withthe first hole and passing through the timing plunger in a lateraldirection, and the second hole communicates with a discharge holeprovided below the passage when the timing plunger moves downward so asto discharge fuel collected in the injection chamber by the lowerplunger.

In accordance with the structure mentioned above, the pressurized oil inthe pressure chamber is discharged via the first hole, the second holeand the discharge hole when the timing plunger moves downward so as torestrict a movement of the lower plunger. Accordingly, the lower plungerdoes not press the body too much, so that it is possible to prevent thelower plunger or the body from breaking.

In accordance with a third invention, there is provided a fuel injectiondevice for a diesel engine for injecting a fuel supplied via a fuelsupply passage and stored in an injection chamber by a lower plungerresponsive to an applied force from a cam through an upper plunger via ahydraulic link and a timing plunger comprising: a branch supply passagehaving an end connected to the fuel supply passage and the other endconnected to the injection chamber; a variable valve to allow fuel toflow within the branch supply passage from the fuel supply passage onlyin a direction of the injection chamber, to open at a pressure equal toor more than a predetermined pressure of the supplied fuel, and tochange a passing area in response to a pressure of the fuel; and aspring for the variable valve to set a moving amount of the variablevalve in response to the pressure of the fuel.

In accordance with the structure mentioned above, the high pressure fueldischarged from the fuel pump of the engine is quickly supplied to theinjection chamber. Since the high pressure fuel supplied to theinjection chamber is supplied to the injection chamber also from thevariable valve within the branch supply passage in addition to the fuelsupply passage, the fuel is collected in the injection chamber with agood response. Since a large amount of fuel supplied to the injectionchamber is injected into a combustion chamber by a downward slide motionat a high pressure, it is possible to increase an output force withoutdecrease of the rotational speed of the engine, and a fast speed and agood response can be obtained.

In accordance with a fourth invention, there is provided a fuelinjection device for a diesel engine comprising a cylindrical body, anupper plunger, closely inserted within a hole of the body, to slide in avertical direction in response to an applied force from a cam, anintermediate plunger arranged below the upper plunger in such a manneras to be coaxial with the upper plunger and forming a pressure chamberfor a hydraulic link with respect to the upper plunger, a lower plungerarranged below the intermediate plunger in such a manner as to bebrought into contact with the intermediate plunger, and an injectionchamber provided in a lower end portion of the body, structured such asto discharge a fuel supplied via a fuel supply passage and stored in theinjection chamber by the lower plunger subject to the force from theupper plunger via the hydraulic link and the intermediate plunger, theimprovement comprising:

a passage, having a large cross-sectional area and formed in the body,for supplying a pressurized oil to the pressure chamber, theintermediate plunger vertically movable in response to an oil pressureso as to make it possible to change a volume of the pressure chamber, atiming spring having an end being brought into contact with theintermediate plunger and the other end being brought into contact withthe lower plunger and vertically moving the intermediate plunger inresponse to the oil pressure, a branch supply passage having an endconnected to the fuel supply passage and the other end connected to theinjection chamber, a variable valve to allow fuel to flow within thebranch supply passage from the fuel supply passage only in a directionof the injection chamber, to open at a pressure equal to or more than apredetermined pressure of the supplied fuel, and to change a passingarea in response to a pressure of the fuel, and a spring for thevariable valve setting a moving amount of the variable valve in responseto a pressure of the fuel.

In accordance with the structure mentioned above, since the oil pressureand the oil amount are supplied to the pressure chamber via the passagefor the pressurized oil, it is possible to quickly move to an earlyinjection timing, so that a response of the engine can be improved.Further, since the oil pressure and the oil amount are supplied to thepressure chamber via the passage for the pressurized oil, no narrow holeis required, so that a variability of the injection timing is reduced.Since the device is constituted by a simple structure comprising theintermediate plunger, or timing plunger, the timing spring and the like,the device is not of a large size.

Further, since the high pressure fuel supplied to the injection chamberis supplied to the injection chamber also from the variable valve withinthe branch supply passage in addition to the fuel supply passage, thefuel is collected with a good response. Since a large amount of fuelsupplied to the injection chamber is injected to the combustion chamberby a downward slide motion of the lower plunger, an output force can beincreased without reduction of the rotational speed of the engine, and afast speed and a good response can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a high pressure injection unit inaccordance with an embodiment of a fuel injection device for a dieselengine of the present invention;

FIG. 2 is a cross sectional view of a timing plunger portion shown inFIG. 1 at a time of rotating under a load and at a high speed;

FIG. 3 is an enlarged cross sectional view of a variable valve portionshown in FIG. 1 at a time of rotating under a load and at a high speed;and

FIG. 4 is a cross sectional view of a conventional fuel injection devicefor a diesel engine.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment in accordance with a fuel injection devicefor a diesel engine of the present In invention will be described indetail below with reference to FIGS. 1 to 3.

A cross section of a unit injector 10 for high pressure injection inaccordance with the present embodiment will be shown in FIG. 1. Arrowsin the drawing show flows of a fluid.

A body 11 is inserted and mounted within a hole in a cylinder head of anengine (not shown). The body 11 is formed in a cylindrical shape, anupper plunger 12 is closely inserted within a hole 11 a thereof, and theupper plunger 12 slides in a vertical direction upon receipt of anapplied force from a cam (not shown). A timing plunger 13 is arrangedbelow the upper plunger 12 in such a manner as to be coaxial with theupper plunger 12, the timing plunger 13 is also closely inserted withinthe hole 11 a of the body 11 and moves in a vertical direction. Apressure chamber 14 is formed between a lower end portion of the upperplunger 12 and an upper end portion of the timing plunger 13, and apressurized oil is supplied here via a pressurized oil hole 11 b formedin the body 11. The pressure chamber 14 has a function of a hydrauliclink for transmitting a vertical motion of the upper plunger 12 to thetiming plunger 13 via the pressurized oil. The pressurized oil hole 11 bis formed in the body 11 at a position above the pressure chamber 14 andnear a lower end surface of the upper plunger 12. In this case, thepressurized oil at about 15 bar to 25 bar discharged from a lubricatingoil pump (not shown) of the engine is supplied to the pressure chamber14.

The timing plunger 13 has a first hole 13 a connected to the pressurechamber 14 in a center portion thereof, and a second hole 13 bcommunicated with the first hole 13 a and laterally extending throughthe timing plunger 13. The second hole 13 b communicates with thedischarge hole 11 c formed in the body 11, below the pressurized oilhole 11 b, when the timing plunger 13 moves downward. Accordingly, whenthe timing plunger 13 moves downward, the pressurized oil in thepressure chamber 14 is discharged via the first and second holes 13 aand 13 b and the discharge hole 11 c so as to restrict movement of alower plunger 16 mentioned below.

A timing spring 15, having an end brought into contact with the timingplunger 13 and the other end brought into contact with the lower plunger16 to vertically move the timing plunger 13 in response to a pressure ofan oil acting on the timing plunger 13 (the pressure chamber 14), isarranged below the timing plunger 13. The pressure of the oil in thepressure chamber 14 vertically moves the timing plunger 13, and thevertical motion changes a volume of the pressure chamber 14 so as tochange an injection timing. That is, the injection timing is changed inresponse to the pressure of the oil acting on the pressure chamber 14.The pressure of the oil acting on the pressure chamber 14 changes inresponse to a rotational speed of the engine. For example, in the casethat the rotational speed of the engine is fast, the pressure of the oilbecomes high, so that the pressure chamber 14 greatly moves downward andthe volume of the pressurized oil entering to the pressure chamber 14 isincreased. Therefore, the injection timing is quickened.

Further, the lower plunger 16 is arranged below the timing plunger 13 ata predetermined interval La apart from the timing plunger 13. A timingspring 15 is brought into contact with an end surface Wa in an upperside (a side of the timing plunger 13) of the lower plunger 16. The endsurface Wa is brought into contact with the body 11 and defines aposition after the lower plunger 16 moves upward. A step portion Wb isprovided in an intermediate portion of the lower plunger 16, and a fuelfor cooling flows into the step portion Wb when the lower plunger 16moves downward so as to cool the lower plunger 16. Further, a front endportion of the lower plunger 16 is formed in a slightly narrow manner,and a front end thereof is formed in a V shape. A fuel injection chamber17 is formed between the front end portion formed in a slightly narrowmanner and the V-shaped front end, and the body 11. A supply orifice 18for supplying a fuel to the injection chamber 17 is formed in the body11 at a step portion Wc constituted by the front end portion formed in aslightly narrow manner. An upper end of a lower plunger spring 19 isbrought into contact with an upper side (a side of the timing plunger13) of the lower plunger 16 so as to pull up the lower plunger 16 andbring the lower plunger into contact with the body 11. A tensile stressof the lower plunger spring 19 is set stronger than a tensile stress ofthe timing spring 15. A lower end of the lower plunger spring 19 isbrought into contact with the lower body 11.

Further, a branch supply passage 21 is connected to a fuel supplypassage 20 provided in the body 11 in such a manner as to branch fromthe fuel supply passage 20 as shown in FIG. 3. A variable valve 22 and aspring 23 for the variable valve are subsequently arranged within thebranch supply passage 21, and the branch supply passage 21 is connectedto the injection chamber 17 via them.

The variable valve 22 opens when the fuel is equal to or more than apredetermined pressure, thereby allowing fuel from the fuel supplypassage 20 to flow only in a direction of the injection chamber 17.Further, the variable valve spring 23 can change a fuel passing area inthe variable valve 22 by setting a moving amount of the variable valve22 in response to a pressure of the fuel. Accordingly, the pressure ofthe fuel supplied to the injection chamber 17 is changed in response toa sudden change of the rotational speed of the engine, and the fuelpassing area of the variable valve 22 is changed in response to thepressure thereof. The fuel at about 15 bar to 25 bar discharged from thefuel pump in the engine (not shown) is supplied to the fuel supplypassage 20.

The fuel in the injection chamber 17 is injected to a combustion chamber(not shown) through a nozzle hole 24 provided in a front end of the body11. As mentioned above, the fuel supplied to the injection chamber 17 isincreased in response to a sudden change of the rotational speed of theengine so as to improve a response of the engine.

On the other hand, a collar 31 is mounted to an upper end of the upperplunger 12 as shown in FIG. 1. An upper plunger spring 32 is arrangedbetween the collar 31 and the upper portion of the body 11. The upperplunger spring 32 has an end brought into contact with the collar 31 andthe other end brought into contact with the upper portion of the body 11and lifts up the upper plunger 12 via the collar 31 so as to define aposition of the upper plunger 12. The upper limit position thereof isdefined by a position brought into contact with a cap (not shown). Theupper plunger 12 receives an applied force from a cam (not shown) andslides against the upper plunger spring 32 in a downward direction.

Next, an operation in the structure mentioned above will be describedbelow.

In the case that the diesel engine starts and rotates under no load andoil at low pressure (e.g., about 15 bar) is discharged from thelubricating oil pump and the like and is supplied to the pressurechamber 14 via the pressurized oil hole 11 b. Accordingly, the timingplunger 13 slides downward against the timing spring 15 a slight amount.At this time, the timing plunger 13 and the lower plunger 16 are apartfrom each other at an interval Lb (not shown) slightly smaller than thepredetermined interval La (La>Lb). At the same time, fuel at lowpressure (e.g., about 15 bar) is discharged from the fuel pump of theengine and is supplied to the fuel supply passage 20. The low pressurefuel supplied to the fuel supply passage 20 is supplied to the injectionchamber 17 from the supply orifice 18 at a lesser amount.

In this state, the upper plunger 12 applies a force from the cam slidesdownward against the upper plunger spring 32 so as to first close thepressurized oil hole 11 b. When the upper plunger 12 further movesdownward, the pressure within the pressure chamber 14 increases fromabout 15 bar so as to slide the timing plunger 13 downward against thetiming spring 15. At this time, since the timing spring 15 is broughtinto contact with the lower plunger 16 so as to move downward together,the pressure within the pressure chamber 14 is not abnormally increased.This downward slide motion slides only the timing plunger 13 downwardwithout moving the lower plunger 16 downward. When the timing plunger 13is brought into contact with the lower plunger 16 due to a furtherdownward slide motion, the timing plunger 13 and the lower plunger 16both slide downward. Due to the slide motion of the lower plunger 16, asmall amount of fuel supplied to the injection chamber 17 is injected tothe combustion chamber at a high pressure. The interval Lb for slidingonly the timing plunger 13 downward without moving the lower plunger 16downward mentioned above delays the injection timing.

In the case that the diesel engine rotates under a high load and at ahigh rotational speed, oil at high pressure (e.g., about 25 bar) isdischarged from the lubricating oil pump and the like and is supplied tothe pressure chamber 14 via the pressurized oil hole 11 b. Accordingly,as shown in FIG. 2, the timing plunger 13 greatly slides downward untilbeing brought into contact with the lower plunger 16 against the timingspring 15. Therefore, the predetermined interval La between the timingplunger 13 and the lower plunger 16 is lost. At the same time, fuel athigh pressure (e.g., about 25 bar) is discharged from the fuel pump ofthe engine and is supplied to the fuel supply passage 20. The fuel at ahigh pressure is supplied to the injection chamber 17 from the supplyorifice 18 and the variable valve 22 at a large amount.

In this state, the upper plunger 12 applies a force from the cam slidesdownward against the upper plunger spring 32 so as to first close thepressurized oil hole 11 b. When the upper plunger 12 further movesdownward, the pressure within the pressure chamber 14 increases fromabout 25 bar so as to slide the timing plunger 13 downward. The downwardslide motion of the timing plunger 13 immediately slides the contactlower plunger 16 together. Due to the downward slide motion of the lowerplunger 16, a large amount of fuel supplied to the injection chamber 17is injected to the combustion chamber at a high pressure. At this time,since the lower plunger 16 immediately slides downward, the fuel can beinjected to the combustion chamber from the injection chamber 17 at ahigh pressure at an early timing without delaying the injection timing.

In the case that the diesel engine rotates under no load and at a highrotational speed, oil at an intermediate pressure (e.g., about 20 bar)is discharged from the lubricating oil pump and the like and is suppliedto the pressure chamber 14 via the pressure oil hole 11 b. Accordingly,the timing plunger 13 slides downward against the timing spring 15. Inthis case, the timing plunger 13 and the lower plunger 16 are apart fromeach other at an interval Lc (not shown) slightly smaller than theinterval Lb mentioned above (Lb>Lc). At the same time, fuel at anintermediate pressure (e.g., about 20 bar) is discharged from the fuelpump of the engine and is supplied to the fuel supply passage 20. Thefuel at the intermediate pressure is supplied to the injection chamber17 only from the supply orifice 18 at a predetermined amount.

In this state, the upper plunger 12 applies a force from the cam slidesdownward against the upper plunger spring 32 so as to first close thepressurized oil hole 11 b. When the upper plunger 12 further movesdownward, the pressure within the pressure chamber 14 increases fromabout 20 bar so as to slide the timing plunger 13 downward against thetiming spring 15. The downward slide motion slides only the timingplunger 13 downward a slight amount without moving the lower plunger 16downward. When the timing plunger 13 further moves downward so as to bebrought into contact with the lower plunger 16, both slide downwardtogether. Due to the downward slide motion of the lower plunger 16, asmall amount of fuel supplied to the injection chamber 17 is injected tothe combustion chamber at a high pressure. Sliding only the timingplunger 13 downward a slight amount, interval Ld (not shown), withoutmoving the lower plunger 16 downward, where interval Ld is slightlysmaller than the interval Lc (Lc>Ld), delays the injection timing.

In this case, when a load is applied to the engine, oil at high pressure(e.g., about 25 bar) is discharged from the lubricating oil pump and thelike and is quickly supplied to the pressure chamber 14 via the largepressurized oil hole 11 b. Accordingly, the timing plunger 13 furtherslides downward a slight amount against the timing spring 15 until beingbrought into contact with the lower plunger 16. As a result, theinterval between the timing plunger 13 and the lower plunger 16 is lost.

At the same time, fuel at high pressure (e.g., 25 bar) is dischargedfrom the fuel pump of the engine and is quickly supplied to the fuelsupply passage 20. The fuel at the high pressure is supplied to theinjection chamber 17 from the variable valve 22 of the branch supplypassage 21 in addition to the supply orifice 18. Due to the to downwardslide motion of the lower plunger 16, a large amount of fuel supplied tothe injection chamber 17 is injected to the combustion chamber at a highpressure. Therefore, it is possible to increase an output withoutreducing the rotational speed of the engine. Farther, early injectiontiming and good response can be obtained.

In accordance with the present invention, a wide range of injectiontiming can be obtained by delays obtained by the predetermined intervalLa between the timing plunger 13 and the lower plunger 16 at a time ofoperation under no load and at a low rotational speed and an earlyinjection timing at a high rotational speed obtained by a state of nointerval between the timing plunger 13 and the lower plunger 16 causedby the pressure acting on the timing plunger 13 at a time of anoperation under a high load.

Since the oil pressure and the oil amount are supplied to the pressurechamber 14 via the large pressurized oil hole 11 b, it is possible toquickly move to the early injection timing, so that a response of theengine can be improved. Since no narrow hole is used, a dispersion ofthe injection timing is small.

Further, since the device is constituted by a simple structurecomprising the timing plunger 13 and the timing spring 15, the device isnot made of a large size.

INDUSTRIAL APPLICABILITY

The present invention is useful for a high pressure injection unit for adiesel engine having a wide injection timing, small dispersion, goodresponse and simple structure.

What is claimed is:
 1. A fuel injection device for use with an engine,the device comprising: a body having a longitudinal channel, aninjection chamber in communication with the longitudinal channel, and afirst fuel supply passage in communication with the injection chamber; afirst plunger, a second plunger, and an intermediate plunger, said firstplunger, at least partially positioned within the longitudinal channel,to receive an applied force to effect a discharge of fuel from thedevice; said second plunger, having a first end positioned within theinjection chamber, to effect a discharge of fuel from the injectionchamber in response to an applied force; said intermediate plungerpositioned within the longitudinal channel and disposed between saidfirst plunger and said second plunger; and a second fuel supply passage,in communication with the injection chamber and extending axiallydownstream of the fist fuel supply passage, to supply additional fuel tothe injection chamber during an increase in fuel demand on the engine asindicated by a fuel pressure within the first fuel supply passagereaching a prescribed fuel pressure, the second fuel supply passageincluding: a valve to control a fuel flow through the second fuel supplypassage such that fuel passes through the second fuel supply passagewhen the prescribed fuel pressure is reached, and a spring, in contactwith the valve, to bias the valve in a closed position and to allow thevalve to open at the prescribed fuel pressure.
 2. A device in accordancewith claim 1, wherein a timing fluid pressure chamber is variablydefined between an upper surface of the intermediate plunger and a lowersurface of the first plunger.
 3. A device in accordance with claim 2,further comprising a timing spring, positioned between the intermediateplunger and the second plunger, to maintain a prescribed space betweenthe intermediate plunger and the second plunger in at least anon-actuated state, wherein the prescribed space defines a range ofinjection timings for the device.
 4. A device in accordance with claim2, wherein the body further includes a timing fluid discharge outlet,and the intermediate plunger has a first passage and a second passageformed therein.
 5. A device in accordance with claim 4, wherein thefirst passage extends between the timing fluid pressure chamber and thesecond passage, and wherein the intermediate plunger is adapted to allowthe second passage to selectively communicate with the timing fluiddischarge outlet during operation of the device to effect a discharge oftiming fluid from the timing fluid pressure chamber.
 6. A device inaccordance with claim 2, wherein the body further includes a timingfluid inlet having a large cross-sectional area, wherein the timingfluid inlet is adapted to selectively communicate with the timing fluidpressure chamber during operation of the device.
 7. A device inaccordance with claim 1, wherein the second fuel supply passage isincluded within the body.
 8. A fuel injection device for use with anengine, the device comprising: a body having a timing fluid inlet, alongitudinal channel, an injection chamber in communication with thelongitudinal channel, and a first fuel supply passage in communicationwith the injection chamber; a first plunger, at least partiallypositioned within the longitudinal channel, to receive an applied forceto effect a discharge of fuel from the device; a second plunger,positioned within the longitudinal channel, wherein a timing fluidpressure chamber is variably defined between an upper surface of thesecond plunger and a lower surface of the first plunger; a thirdplunger, having a first end positioned within the injection chamber, toeffect a discharge of fuel from the injection chamber in response to anapplied force from the second plunger; a timing spring, having one endcontacting the second plunger and another end contacting the thirdplunger, to operatively separate the second plunger and the thirdplunger by a variable space when the second plunger is subject to anapplied force below a proscribed level, wherein the variable spacedefines a range of injection timings for the device; and a second fuelsupply passage, in communication with the injection chamber andextending axially downstream of the first fuel supply passage, to supplyadditional fuel to the injection chamber during an increase in fueldemand on the engine as indicated by a fuel pressure in the first fuelsupply passage reaching a prescribed fuel pressure, the second fuelsupply passage including: a valve to control a fuel flow through thesecond fuel supply passage, wherein actuation of the valve is determinedby the prescribed fuel pressure within the first fuel supply passage,and a spring, in contact with the valve, to bias the valve to a closedposition and set the prescribed fuel pressure necessary to open thevalve, wherein the timing fluid inlet is adapted to selectivelycommunicate with the timing fluid pressure chamber during operation ofthe device.
 9. A device in accordance with claim 8, wherein the bodyfurther includes a timing fluid discharge outlet, and the second plungerhas a first passage and a second passage formed therein.
 10. A device inaccordance with claim 9, wherein the first passage extends between thetiming fluid pressure chamber and the second passage, and the secondplunger is adapted to allow the second passage to selectivelycommunicate with the timing fluid discharge outlet during operation ofthe device to effect a discharge of timing fluid from the timing fluidpressure chamber.